100-line all relay system



y N. H. SAUNDERS 2,325,151

IOQ-LINE ALL RELAY SYSTEM Filed D66. 2, 1940 8 Sheets-Sheet 1 dddo dz ddd' Ill-h.

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July 27, 1943.

N. H. SAUNDERS 2,325,151 IOU-LINE ALL RELAY SYSTEM Filed Dec. 2, 1940 8 Sheets-Sheet 2 Narmanfiiazmiers.

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8 Sheets-Sheet 8 N. H. SAUNDERS loo- LINE ALL RELAY SYSTEM Filed Dec. 2, 1940 July 27 1943.

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Patented July 2' 7, 1943- 12,325,151 g I'M-LINE RELAY SYSTEM I I iN-orman H. Saunders, Chicago, lll lassignor to Kellogg .Switchboard' and ,Supply. Company,

Chicago, 111., a corporation of Illinois Application December 2,1940, Serial No. 363,175 4210mm. (ol ve-17.)

The present invention relates in. general to automatic telephone systems, and more in particular to automatic telephone systems of the relay type, in which connections between calling and called lines are established solely by means of relays. The general object of the invention is to provide a new and improved system of this characterhe system disclosed'herei-n is of relatively small size, having a capacity of somewhatover one hundred lines, and is well adapted to the needs of a small town or comm-unity. A telephone exchange. for use in a situation of this kind is required to provide for various typeset service, as is well known. For example; the

system may include party lines and rural lines.

in addition to individual lines, and the exchange must therefore provide suitable signalling ar r'angements such as semi-selective ringing, code ringing,v and reverting-call ringing Wherebya party line subscriber may call another subscriber on the same line. There mayalso be several business establishments in the community served by private branch exchanges and the'automatic exchange must therefore be equipped groups of trunk linesior handling calls to and from such private branch exchanges. rare case of an isolated community, the ex-E change must also be provided with a group of trunk lines extending to a toll center, through which connections may be obtained with other exchanges. foregoing will suflice to give a general. idea of the nature of the exchange and the facilities provided therein. l "All connections" through the exchange are established by means of link circuits, each link comprising a relay type finder and arelay type connector. The finders have commonaccessito all subscribers. lines and trunk lines entering the exchange. An allotter is provided for the purpose oi assigning idle finders to calling lines. The connectors likewise have common access to all the subscribers lines and. trunk lines and employ a variety of novel circuit arrangements,

wh reby they are adapted to complete connec tions to all of the difierent kinds of lines and trunk lines terminating in'the exchange;

The allotter normally mainta'ins a finder, or link circuit, in assigned condition ready to handle the next call; When'the" call comes in, the assigned finder connects with the calling line and thus extends it to the associated connector. The calling subscriber then :dials the number 'ofthe called line, which'may have from. one t'o. four Except in the While not necessarily complete; the

' line, there beim other telephones such, as the telephone at station '8 connected tothe linen The ringers "atthese telephones may bexbridged' .55 across the line, or asindic'ated herein the ringdig-its, depending on the kind of'lineor station being called. In any case the-connector responds in the proper manner to complete the connection to the called line, performing an automatic trunk selecting operation in case the called number is the number of a trunk group, and effects the" necessary signalling operation if the called line, is idle, or if a trunk line isavailable'in'the case where a trunk group is called- Otherwise the calling subscriber is given a busy signal. foregoing applies also in the case where the ;cal1-. ing and called subscribersare on the same'party line, except that the busy signal does not-have the usualsignificance.

It will be understood therefore that the-new system 1 disclosed herein includes a considerable number of novel features, particularly desirable l I in a' smallsystem of thekind disclosed herein, but not necessarily limited to us'e'in small ex-' changes. "These features will be pointed out more in detailhereinafter in the coursexof a detailed description of the exchange and. its opera-.-

eference may now be made to the "accom anying drawings, in Which Fig. 1 shows a subscribers line and individual ine equipmentfa number of finder control res lays, a' finder (not complete), and an allotter;

Figs. 2, 3, 4 and 5 show a connector (complete) except for some of the group relays) Fig. 6 shows'eduipment common to the exchange for use in selecting idle trunks When trunkgroups are called;

Fig. 7 shows a trunk' repeater for use -on a trunk line extending to'a toll center;

Fig. 8 shows the terminal equipment-0f trunk line at the toll center; and

9 shows a number of. interrupters which such arecommon to the connectors in the exchange.

, General desc ipt n Referring to Fig. '1, the reference character indicates a subscribers' station, which may be of' any suitable common battery type. The telephone at station'A is connected with the .eX-

change over a line comprising conductors 2 and 3. Atthe exchange the line is provided with the. individual line equipment comprisingthe linerelay the cut-off relay 5, and the lookout relay I. I

The line of station A is shown herein as a'party ers at some of the telephones maybe connected between one side of the line and ground while the ringers at the other telephones are connected between the other side of the line and ground.

All the lines entering the exchange are divided into groups of ten lines each. The line of stations A and B is assumed to be line #1 of group #1 and its telephonenumber therefore is 11,.

insofar as the line selecting digits are concerned. The complete telephone number of each station includes an additional code selecting digit. Each 7 group of lines is divided into two sub-groups, lines I to 5 comprising the first sub-groupandi lines 6 to 0 comprising the second sub-group.

For the purpose of controlling the finders, each j j group of lines isprovided with three control'relays, the control relays for the first group being and the calling line is extended to the connector trunk by way of the front contacts of the switching relay.

The trunk conductors 60, GI and 62 extend to .Fig. 2, where they terminate in the connector of inFigs. .2 to5, inclusive, and comprises the miscellaneous control relays to H2, inclusive,

Fig. 2, sea to 396, inclusive, Fig. 3, and 493 to 4136,

inclusive, Fig. 4. The functions of these relays l will be explained in the course of the general indicated by reference numerals I9, 20 and 2|.

Of these relays, relay I9 is common to the first sub-group, relay 20 is common to the second sub-group, while relay 2! iscommon to all the lines of the first group. The drawings also show the control relays 22, 23 and 24 which are asso-" ciated with the second group of lines.

The control relays exercise their control over the finders through the medium of an allotter,

which determines the link circuit and finder to be used on each call. The allotter comprises relays I00 to H36, 'inclusive,and relays III to I20, inclusive, and as shown herein is wired for ten link circuits. Tlus number can be increased by adding more relays to the group I i l to I20, these relays being individual to the respective link circuits. V

Relay H is a connecting relay which is individualto the first link circuit. There is a similar relay for each of the other link circuits.

As previously stated, each link circuit comprises. a finder and a connector. Each finder comprises a number of group relays equal to the number of groups of lines, five units relays, and a switching relay. The drawings shows-only one group relay, being relay M, which is assumed to be the first group relay. As shown, relay il only has four sets of contacts, but it will be understood that ten sets are provided, one set for each of the ten lines of the group. Relays 5! and 52 are the first and second units relays, the

adapted-to extend the first two intermediate trunks, to which lines Ii and it are connected when group relay 4! is energized, to the contacts of the switching relay. Similarly, the units relay 52 is adapted to extend thethird'and fourth intermediate trunks, to which lines l2 and H are connected-when group relay 4| is energized. If the calling line is a line in the first sub-group, line H or l2, for example, the switching relay is not energized and the calling line is connected to the trunk line extending to the connector (conductors as, 6! and 62) by way-of back-contacts of the switching relay; If the calling line is a line in the second subsgroup, line is or'il', for

example, the sub-group control relay such as description. The connector also includes the two timer relays Sill and 462, Fig. 4. Relay 461 is, a'code 'switchingrelay. Relays Ml and M2 respond when the first digit dialled'is the digit 2 and; provide for two digit group selection as well as for controlling the code switching're'lay. Relays 498, 409, and H0 are counting relay con trol relays, and relays to 5l0,:inclusive, are counting relays. Relays 5H and 5 are connecting relays for connecting up the common trunk selecting equipment shown in Fig. 6 when a trunknumber is called. Relay 5l3.is a relay in another connector. corresponding to relay 5l2;

The connector is also provided with as many group relays as there are groupsof lines, similar to the finder. Of these group. relays the first, eighth, and ninthare shown in Fig. 3' where they are indicated by reference characters 3H, 3!!! and 319, respectively. .In addition tothe group relays, there are five units relays and a switching relay. The first two units relays are shown and are indicated by reference characters 32! and 322, respectively. Relay 301 is the switching relay; It will be understood that each group relay in the connector has ten sets of line connectingcontacts, like the group relays in the finder, although the drawings only show four sets of contacts on each group relay;

Fig. 3 also shows a'number of lines which are accessibleto the connector of the first link circult and likewise to the connectors of the other link. circuits. These lines, will bev described briefly.

The line comprising conductors 2', 3, and 4' is the line of station A and these conductors connectfto the same numbered conductors in Fig. 1.

Thetelephone number of this line is 11, as previously stated, and it is reached'by way of contacts of the first group relay 3| I, contacts of the first units relay 32I, and the back contacts of the switching relay 391;

The line comprising conductors 326, 32! and 328 -is a party line, or rural line, and there may be twenty stations such as C and D on the line.

The telephones at these stations are of the common battery type and the'ringers are bridged line relay 3G9 and the cut-off relay 388. The line is accessible by way of contacts of the eighth group relay 3 !8,.contacts of the first units 32!,

and the front contacts of switching relay301 and V the line telephone number the'refore is 85. Each stationon .theline has-one ortwo additional di its in its complete telephone number to control thering ne I The line comprising conductors 329, 330, and SM. is a trunk line and is the first trunk line of a. group of five trunkllinesextending to a rivate br nch exchan e. Thezsecond trunk line of the roup is. the trunk line comprising conductors 33 333K311! 334., They other three-trunk lines of the group are notrshown. .Each trunk line i providedwit individualline equipment the s m as a subscriber's-line. At the branch exchange end the trunk lines may terminate in telephonesor in, a PJBLQX switchboard of any suitable and well known'type. The telephone n m er of th s trunk-line gIQllP'iS8l." When this number is dialled the firsti'dle trunk of the r up is connec d with andis s na led uto.- matically. Trunk lines '82 to 85, inclusive, may

e ch ave an individual 'listingalso.,.which in- The equ p n atrthe e chan e vendis show in Fie- Relays 2! and are the usual line and cut-off relays, The conductors 3.35, 336,.and 33' co ne t to c ndu t rs 1-2. 123- and 1 4, ir sp v wh h t rmi te in the rep a er mprising relays 191 to l ipinclusiveyand the repeating coil R. Relays H6 to. llalinclusive, are

relays of other repeaters; and'correspond to relay m4 of there eater shown. r The. inter exchange;section of the trunk line comprises the twc conductors; 1'25 and 12$,which extend to Fig, 8,:zwhere -thetrunk line is pro.- vided withsuitable terminal equ pment. This equipment is located at the toll center and comprises relay Bil l to 83,6; inclusive, a repeating coil R}, a trunk jack Jl, a dialling jack J2; a line lamp Li, a busy lamp L2, The operator is provided with cord eircuitgwhioh are of well known type" and are not shown herein. The ooerator al o has a ea-11mg; device CDywhiehm y be con, nectedto the dialling lack of a trunk line by means of the plug P. It will be understood that the trunk line maybe multipled to other operators positions inkhown manner.

Referring now to: Fig. 6, the equipment there shown is common to all the. connectors and. may be momentarily connected to any connector to enable the selection of an idle trunk when a trunk group is called. The. equipment comprises um r of relays andcireuit connections which will be explained briefly.

Relays. sea and, cs2. as. associated with the.

r up i n s whi h extend to the toll center, the former relay, bein a'connecting relay and the latter an all trunk busyrelay. Relay 62H. is energized momentarily. when the trunk group called and connects the-marking conductors S4} to 645, inclusive, tefconductors 735i to 18mmclusive, which extend to Fig, '7: where theytermin-ate in contacts. of'thebusy relays lh l and 'lli to H9, inclusive. Ch.nductor 1313 also ex-.-'-

Relay ,133 is the connecting, relay and relay 3 GM is the'alltrunk busy relayassociatedfwith the groupof private.branchirexchange"trunks;

. ductor 33!, Fi .3, o f-the,first trunk: line of the group, and terminal 632is connected to test con;

' ductor 334 of the second trunk line' ofthe group;

and so on.

Relays 620; 62k. and 6 22 :are'also associate zd with the group of private branch exchange trunks.- These relays function when atrunk of this group is connected with' to transmit an impulse to the connector in use to start .the ringing operation.

Fig. 9- shows three, special interrupters 1505; 336 and 631 which will *be referred to as lthe Pickup,, lock, and reverting call isignal inter rupters, respectively. Theyiare commonttolall the connectors. As regards the connector shown herein, terminal 2l3, Fig. 2, and terminals 348 and 349,:Fig1 3 are wired to terminals 6H1; 698', and609, respectively; Fig. 9.: The other connectorsjare wired to Fig. 9:in the: same manner. 5 The reference characters 616 and-ell indicate two code ,interruptersf .These' interrupt ers are the first and eleventh code interruptersrespectively. There; are. eighteenmore code interrupters, omitted for lack'of space in the draw-' ings'each generating a differentcodeb All the code interrupters, also interruptersflfid', 605', and

6531: are assumedto be continuouslyiro tating at slow speed and in synchronism-with each other.-

'It will be understood; however, thatin'a'ctual practice suitablev arrangements may be made for starting up this equipment only when required for rins n purposes. r i a Detailed 'czrpl nctio qrstotion A 7 culling, station 30, I The operation ot-the system will now-be 'clescribed. For this purpose it..will first beassurned that I the: {subscriber at station A desiresto-calhthe subscriber atstationCL-Tfhe line number of. the party 'line to which, stat-ion ZC- is H connected is 86 and-assuming that. station .C

has been; assignedthe first of the twenty different rin ing codes the complete telephone humabridge-is closede-cross-the lineconductorsl:

and 3 and a circuit is lcompletedfor the line.-

tends between Figs. 6 {and 7: and serves. to ener-,..

relay 5. Upon energizing, relayh-xgroundsthe individual; marking conductor: lit and also:

groundfsconductor |l;.whi'ch:is common to lines I. (.05 ofthe firstgroup, oryto thefirst sub-group of thefirst group"; The grounding of conduc tor completes a. circuit'for'the first groupccntrolrelay 2! which maybe. traced from ground byway-of-contact in. of the line relay 5', can:

7 tact l.3;-conductor" I'Lwinding of subgroup con trol' relay l9; contacts'lz, winding offirst'group relay 2i, contact .213,:.concluctor 3&9, 'contactsfof grouprel'ays: not shown,- contacts oiithe second grouprelay-controlled at 25}, contacts of the first contact 28;. .Atithe same time, relayZl disconnects. battery;- from-conductor 30; which pre accordingly battery is maintained disconnected from conductor. 3| .for a brief intervalsufiicient for theoperation' of the allotter in assigning a link circuit for the next call.- c a The operation of the allotter is initiated by the deenergization of relay H, which closes a circuit 7 windings. When relay I03 falls back the circuits of both windings are opened, at contacts 83 and 84. The circuit of the upper winding ofrrelay HEZ is also' opened at contact 33 butthis relay remains energized over a branch ofthe previously traced circuit, said branch extending. from contact 18 through the lower winding of relay hi2 to'batteryf Wherfrelay I93 deen'ergizes it closes a circuit for relay H 2 extending from the grounded conductor 64 by way of. Contact 82, contact 9!, and

winding of relay H2 to battery. On energizing;

relay H2 prepares a' circuit for relay H3, and locks itself at contact 97$; .Also atcontactQS relay HZ' opens the locking circuit of relay HI, which deenergizes and breaks the circuit through the lower winding of relay H32. The latter relay accordingly deenergizes also. i a

It will be convenient atthis point to consider the operationof the allotter responsive to succeeding calls before continuing with the explanation of the establishment of the connection from station A. When the next call comes in relay N39 is energized as before and closes a circuit extending from ground by way of its uppercontacts, contact $5, contact 538, winding of .relay 13$,contact 86, contact 94, contact 98, and conductor IN to the connecting relay in the second link circuit, said connecting relay corresponding to relay 'H of the first link circuit. 7. Upon the energization of the second connecting relay, the finder of the second link circuit is operated to connect with the calling line. When the holding conductor of the second link circuit is grounded, ground is applied to common conductor 65 and relay [M is energized, also relay liil, with results previously described. Upon the deenergization of relay I88, the circuit of the second connecting relay is broken and it deenergizes, breaking the circuit of relay 154. The deenergization of the second connecting relay also closes a circuit for relay H33, extending from the grounded holding conductor of the second link circuit by way of a conductor corresponding to conductor i5, contact of the second connecting relay corresponding to contact 19, conductor Hi], contact 97, contact iii, contact 18, and lower winding of relay Hi3 to battery. ,Upon energizing, relay H33 closes a locking circuit for itself at contact 83 and closes a circuit for relay H3 atcontact 82. The latter circuit extends from grounded conductor 65 by way of contact 82, contact 95, and winding of relay H3 to battery. Upon energizing, relay H3 prepares a circuit for relay H4 at contact I22, locks itself, at contact I23,.and at the same contact breaks the locking circuit of relay H 2.7 Re- 1 lay H2 accordingly deenergizes and breaks, the initial energizing circuit of relay H33, said vrelay remaining energized over its locking circuit, which now energizes relay IE2. Relays; H32, H33, and H-3 remain energized awaiting the next call. When the third call comes in,:relay ltd enere contact 8%,;contact 94, ccinteictBd-fccntect i and conductor l2! tQ-the'conn ctin -renne the third link-circuit. The third connectin relay accordingly energizes and brin s ab ut 139199:- eration of the finder in the third linkcircuit to connectwitn the caningline, .Gcnductor 55 rounded as befor causin the cners zati n oi relays, and and i it! and the deciiereizaticn of relay Ice. 1 The latter relaytbreaksythc circuitry? the third c0nncctingrc1ay, .which deencrgizes andbreaks thecircuit oi relay Him-also placing ground on conductor, iz-iitaT fi'latt opc at" n completes a circuit for the upperwinding; ct 58% lay Hi3 extending by way sroiindcdcon nct r 52%; contact 7 i at; contact -.|9 ,;lccntact- 18-, contact. 84; and iupnerwindins of relay N53 to batte y;

Current now. over this circuiti cnc eizesrclay its by differential acticn-, whi.1e.a bran h. c rcuit through the lower winding 01 relay 19? holds this relaycnergized, as Previously explain d.- The tide enersization of relay 03 closes at circuit icrrelail H4, extending from grounded .conduotorjfil by 7 way of contact 82, contact IZZ.-'.&l11 ..WiIiI B -f 1' ay Hi to battery.- vUpon energizin re ay 1.114 prepares a circuit for relay H5. atcontact I28, locks itself at contact l 9 ,-and atthctscine onr tact opens the lockingcircuit ofrelay 1 i3, lllpcn deenereizine, re ay 5 it breaks the; holdin circuit of relay its and this relayeccording ydcener gizes also.

From the explana "on so far it will be ated that relay i583 is an impulsing relay for con- Y trollin th r ays! to I28, in nsivawtthe allotter, being assisted inc-this innctionby relay 102'. Thesereiays are energized and deencrs zed responsive tethe first cail, are e er ized sive to. the second call, deenergized respcn iyc to the third call, etc. Bel -y Jill is control dcyer a special circuit in luding, contact '8! of relay its. Of the remaininerelays 'tttc 23. infill- 3 sive, the even numbered relays areccnt led at the back contact 82; While the o d numbered relays are controlled-at the ircntcoritm v g When the fourth call comes re ay Jill-east" gizes and closes a circuit over conductor .1312. in the connecting relay of th ourth link .c r t. This relay according y energizes and the, of the fourth link circuit connects nithcthe call me line. Conductor amended on are: vious calls and-relays 1M and-iii] are ener ized.- Relay we then decnereizes and eaks the cir uit of the fourth connectin relayv re ay emereizes, around is applied to conductor 43! Y and a circuit :is comcicted through the i iwer winding of relay its. 011 energiz ng,- reley 1.193 locks :itseif at contac 83 and at contact 32 a circuit for relay. l .19 ener izin ice-lay 31.5 locks itself and break thelockine circuit or relay lit, which deenergizes d brea s the initi en ere'iz-ine of relay 1533, n t ogre-lay 872 to cn-g ergize over the locking circus o relay 1563- lays m2, its, andji-b are new ener ized condition. t A 7 t It will be assumed new that the a ninth linkrcircuits, inclusive, are busy. .Accor there-will be aground on conductor, i 33 through a bae-kcontact of t ie f1 connectingrelaym t; r p n abh kt l tat ifogt cameraman in r y and c ndut g is vit to 131', inclusive; willbe similarlyel'ou d d I I When .i

as ii d r the tore cine circumstances, a 'circuit is completed ,ov'er the gizes and closes a circuit extendinethrougnits. upper contacts; contact Bil; contact QiLfrelh? Hi6,

, winding of relay I03, which locks itself and operates relay 1. Relay II'I locks itself and breaks the locking circuit of relay IIIG, which deenergizes and-breaks the initial energizing circuit of relay I03. Relay I02 now energizes over the locking circuit of relay I03.

{On energizing, relay I02 completes a circuit for-its lower winding and for the upper winding of relay I03, said circuit including the grounded conductor I35. 'Relay' I03 accordingly deenergizes 'by diflerential action and operates relay I I8, which looks itself and breaks the locking circuit of relay III. On deenergizing, the latter relayopensthe holding circuit of relay I02 and this relay deenergizes. a

"On deenergizing, relay I02 again completes a circuitfor'the'lower winding of relay I03, this time over grounded conductor I36. On energizin'g',-' relay I03 locks itself and operates relay II9, which locks itself and breaks the locking circuit of relay H8. on cleenergizing, relay II8 breaks the initial-energizing circuit of relay I03, whereupon relay I02 energizes in the locking circuit of relay- I03.

On energizing, relay-I02 closes a circuit for the upper-winding'of-relay I03 over grounded conductor I31, thereby deenergizing said relay, relay I02 holding up over its-lower winding. The deenergization of relay I03 operates relay I20, whichlocksitself at contact I38 and breaks the locking circuit of relay H9. On deenergizing, relay II9 breaks the holding circuit of relay I02, which deenergizes. In energized position relay I20 prepares a circuit at contact I39 for the conriecting relay of the tenth link circuit.

The foregoing operations in which the allotter searches foran idle link circuit take place very rapidly, well within the deenergizing time of relays I04 and IIII. When the next call comes in, relay'I00 energizes and closes a circuit over conductor I4I for the connecting relay of the tenth link circuit. This relay accordingly energizes and the finder of the tenth link circuit connects with the calling line. Ground is applied to conductor 65-as previously described and relays I04 and IOI are energized. When relay I deenergizes, the circuitof the tenth connecting relay is broken and this relay falls back, grounding conductor I40 and closing a circuit for the lower winding of relay I03. Relay I03 energizes, locks itself, unlocks relay I20, and prepares a circuit for relay III. Relay IIIenergizes and locks itself over the chain circuit as soon as this circuit is closed by the deenergization of relay I02. The deenergization of relay I also breaks theinitial energizing circuit of relay I03, whereupon relay I02 energizes over the locking circuit of relay I03. Assuming now that the first link circuit has become idle, there willbe no ground on conductor I42 and'relays I03 and I02 will remain energized, maintaining the first link circuit assigned for use on-the next call; Subsequent calls are handled by the allotter in the manner described.

'In case a link fuse is blown, the link is passed up by'the allotter as in the case when the link is busy. It may be assumed, ior example, that thefuse for the first link is blown, which means that battery is disconnected from the various 'relays 'of the link, including relay "II.. .When the next call comes in, therefore,- and relay. I00 is energized, the saidrelay cannot close the .usual circuit through relays I06 and 1 I. Relay I00, not beingenergized, the branch circuit through relay I05 is effective and this relay grounds; contact 19 of relay I02, thereby .cornpletinga, circuit for holding relay I0'2and deenergizingrelay I03. On deenergizing, relay I03. breaks the circuit of relay I05 andcloses. a' circuit for relay II2, thev latter relay locking and opening the circuit of relay I II. When relay. I05 deenergizes it opens the holding circuit of relay I02,- which vdeenergizes andcompletes the usual circuit forjconnecting relay of the secondlink circuitover conductor I2I. .That is, this circuit is completed provided the fuse for the second link circuit is all right. If the fuse is blown the circuit will not be completed, relay I00 will not energize,,and relay I05 will operate tocontrol relays I03; and I02 the V manner explainedj. i When all thelink circuits are busy there is no ground on conductor 64 and the allotter is thus prevented from performing futile searching operations. When the last link is takenfor use by energization of its associated connecting relay such as H, the last connector ground is removed from conductor 64. Relay I00, however, energized in series with the connectingrelay, maintains anotherground on conductor 64 until it falls back upon the deenergization of relay I00. Thus relay TI is maintained energized untilthe call is disposed of by the allotterand false operation of the overflow meter MI is prevented. If another call comes in before a linkcircuit becomes idle, the energization of relay I00 will operate meter MI. Returning now to the connection being set up from the calling station A to the called station C, the calling line has been extended to the connector or" the first link circuit by operation of the associated finder and the line relay 204 is energized over the calling line loop in series with the impedance coil 203. .Relay 205 is energized as previously explained. Relay 201 is also energized, being connected to the ground test conductor 02 throughcontact 243 of relay 208. In energized position, relay 201 removes the first link circuit groundfrom conductor 54 at contact 230. Relay 20?;aiso grounds the holding conductor 260 at contact 238. Dial tone is connectedto the calling line over a path which may be traced from conductor 60 of the calling line by way of contact 2I5, contact 225, condenser .282, contact 245, conductor 26?, contact'325, contact356, conductor 483, contact 408, and contact 446 to the conductor labeled Dial tone in Fig. 4, which extends to the dial tone. generator. The calling subscriber is informed bythe characteristic tone in his receiver that he can start dialling the digits of the called numbers. 1 The first digit in the number of the called station C is the digit 8. When the calling device at station A is operated in accordance with this digit, a s'eriesof eight interruptions is produced inthe calling line loop, causing the line relay 200 to deenergize momentarily eight times and transmit a series of eight impulses to the counting relays in Fig. 5. The impulsingcircuit may be traced from-ground by way of contact 2I0of relay 20I, contact 225 of line relay 204,

' contact 237, conductor 266, contact 35I, contact 3'41, co uctor 3:15 eon-tact; 5'20; .eonductor 1316;,

contact 451, contact-454, contact 45'l,"conductor 43 i, and windingof-first eountingr'ela'y 581' to battery. Thisis the circuit over Which-the'first impulse is-transmitted, The othenimpulses are transmitted over the same circuit except that it includesa cli-fierent counting relay for ecah successive impulse, as will beexpl'ained. The slow acting change ever relay 306,-Fig. 3, is connected to conductcr 316' of theimpulsing-circuit and energizes on the {first impulse, remaining energized thereafter until the series of impulsesis completed. At its contact 351, relayeec short circuitsthe impedance coil 203 to improvethe circuit. 'At; contact 358;relay 305* shunts contact 528. Relay-4651s also connected dialling to conductor 516- and energizes respcnsiveto the first impulse. This relay-is notslow acting but is held energized throughout the series" of impulses over conductor Q,'Whl(}his connected to I groimded conductor 260 at c'ontactSBO ofrelay e 3%.- Conductor 260, it will be reca1led, ha s been I conductor 388, contact 516,,and1winding or relay tail to battery. The, locking circuit becomes effective as soon as the firstimpulse is terminated,

whereupon relay H is. energized andtransfers the impulsing circuit torelay iiiii by way of contact 65?, conductor 485, and contact-W. 1

Counting relay 502 is energized by thesecond impulse, prepares the circuit iorrthe third counting relay 563 at contact iii, and closes a locking" circuit for 'itself'at contact 522'. This lock ing, circuit is the saine' as the lockin-g circuitoi relay 58!, previously traced, except that it in.- eludes conductor 49G, relay 409, and contact 453 M3, contact 444-", conductor tee, Contact 52 as relay 5E8, 'conducter'382, and winding of relay At the termination of the second impulse relay 3E9 energizes in series with relay 532 and trans.- fers the impulsing circuit to countingrelay 593 by way of contact 464,:cenductor 486 and contact 52!. Relay 409 also breaks the locking circuit of relay 561 atcontactASt, whereupon re: lays Siii and MD aredeenergized. :The, circuit to battery through relaysAiO and 5M is'of high impedance and accordingly is:shunted by a resistance as indicatedin the drawing in order to suppress sparking at contact 455. The other two locking circuits are similarly provided with sparkv suppressor circuits.-,

Counting relay 503 is energized by the third impulse, preparesthe circuit of relay 56 3 atcon-,;. tact 5'23,- and. closesa locking: circuit foritself; over contact 524, conductor 45!, relay 488-,and contact l59. At the termination of the impulse relay 3E8 energizes in series with'relayjilt and transfers the impulsing circuit to relay 584 by way of contact- 45!, conductor diil, and contact 523. Relay cflilalso breaks. thelocking circuit of relay 502 at contact 453,; thereby deenergizing relays 5E2 and 409., 7 The operation of the counting relays continues in. this manner untilfinallycounting relay'EllS is energized. by the-eighth impulse; Relay 508 looks. itself at contact 525, overtconductornfieand relay 469-, 'andrtne latter relay energizes ir'i the locking circuit at .theterminationof the ime pulse. The preceding counting relay 531' and relay Milared-eenergized by the opening of con tact 4560f relay 489. 'Thusatthe completion or i the series of impulses relaystfiii and 409" remain energized.

"Relays mati restore at the end es the" series of impulses: and the former relay closes-1a which extends from grounded conductor sec-by way of contact Slit, conductor Mi Contact Mite of relay 4%; contact 43?,- cent'acts controlled iat 3i8 te= battery; Om energizing, relay than nects conductor 882' to ce-nductor 5539' atcontact 38?, thereby closing a circuit for'r'elaycrewman extends from thegroundedlconductor'alfby way, of contact 361, conductor-4G9, and vvinding' of relay 535 to battery Upon energizing; relay 485 looks itself at contact 442 togro-unde'd conductor 2% and thereby'ext'enels ground back over v initial energizing circuitto the group relay Thus relays 4G5 and 348 are locked in parallel V togrounded conductorrfi jl Other results of the'energizatien of relay 485 that may be noted at this time are the opening of theclial tone circuit at contact Attend the opening or" thelocking circuit of relay's ,fiilfia'nd 439 at contact 24!.

prepared for receiving the next series of pulses. Also at contact 1 relay 405' 'disccne nects the marking circuit from thegroup mark; ing conductors and connects it instead; to contact @553, whence his later extended tothe units marking conductors. I

A a result of t-heienergization' of the group relay 3J8, the ten lines 82 to 83', inclusive, are

c'onnecteclfinto the link circuit. One of these lines is line 83} the line of' the cailedstat'i'on C:

he second digit of the. called number-"is the digit 6: When the calling subscriber dials this digit, 3. series of six interruptions is produced in the calling line loop and'the line relay 2% is momentarilyv deenergized. six times to transmit a series'of siximpulfsesto' the'co-uhting relays;

These'impulses are transm'ittedpver the samecircuit 'as'the'precedin'g series. Relays-336 and 466 energize as before and remain energized throughout the series of impulses. Relay 6L111 fact, locks itself to conductor 25%)- at QOhtact 4 53, relay 495 being energized.

The counting relays respond to th secon se ries of impulses the'same as ,hefore except' that the locking ground issuppliedt'o contacts of'ree lays 458, M19, and 459 fromconductor 2'65 byway of contact 44? of relay 4%, The last impulse of the series energizes relay 5%, which locks it'- 'self at contact EZTin series with relay 458i The second series of impulses therefore v I results in'tlie energization of relays 5% and 488. V At the end .of the second series of im uls s relay 32-6" falls back; but relay lliaren alnsen. erglzed, the latter relay being locked throu h 1 m relay 5 a p evi uslrmem tioned; Upcn 'deenergizing, ieIayttFClOS'es aj circuit for the-units relay 321' whichextends from" grounded. conductor 25%? by wayofco conductor {48 contact 552 of relay contact 431, contact Ms, contact 459, conduct-ar ses; tact 523 of relay 5 86, conductor 311,,and winding" of relay" 32F to battery. Upon' energ zin ay: 3Z5 'connects the now rounded condtctdr V I Relays SBB'and 6S9 accord; I ingly' deene'rgize' and the counting relays are" thus tactics; I

3.11 to conductor, 4,16, andthereby closes a circuit for relay 404 extending over conductor 415 and through the winding of relay 404 to battery. Upon energizingrelay 404 locks itself and relay 321 togrounded conductor 260 at contact 438.

It is necessary now to explain the operation of relay 300. This relay is energized during the dialling of the first digit in parallel with counting relay. saidrelays being connectedover conductor 314. When relay 3001's thus energized, it looks itself at contact 3l4 over conductor 418, which connects with the counting relay locking circuit Fig. 4. Accordingly relay 300 is unlocked and deenergized along with. counting relay 508 followingthe energization of relay 405. The ope'ration of' relay 300 responsive to the dialling of the first digit is without effect. Relay 300 also energizes in parallel with relay 506 when the second digit is dialled and locks itself over conducthesame .ason the, previous digits, and; closes a circuit for testing the calledline, said circuit extending from grounded conductor 250 by way of contact 359, conductor 258, contact 228 con ductor 259,-upper-winding of test relay 303, and

' contacts of relays301, 32'! and3l8 to the test gizing the units relay 32 I, a branch of said mark- Relay 301 is thus energized in parallel-with relay 32I. On'energizing, relay v301 closes a locking circuit for itself which extends to grounded cona ductor 250 by way of contact 354, conductor 411, and contact 442 of relay 405 to conductor 250.

Returning now to relay 404, thefenergization of this relay opens the marking circuit at contact 431, and opens the locking circuit of relay 406 at contacts controlled by'contact 438. Relay 406 accordingly.deenergizes, breaking the locking circuits of relays 506, 408, and 300, which deenergize also. In addition tothe foregoing, relay. 406 closes a circuit for relay 433, extending from grounded conductor 250 by way of contact 441, contact 430, conductor 285, contact 224, conductor 288, and upper windingof relay 403 to battery. Upon energizing, relay 403 looks itself at contact 428 and prepares a holding circuit for relay 405 at contact 43L I The energization of units relay 32| selects lines 8| and 86 of the ten linesBl to 80 selected by the group relay SW. The energization of the switching relay 301 selects line 85 of the two lines selected by the units relay. The line. selection has accordingly been'completed and the equipment is'ready for the dialling of the third or code selecting digit.

The code selecting digit is the digit 1. When the dial at the calling stationis operated in accordance with this digit, a single interruption is produced in the line circuit and the linerelay 204 is momentarily deenergized once, there by transmitting a single impulse over the impulsing circuit and energizing counting relay which locks itself in series with rela 440 at the termination of the impulse, The count ing relay holding circuit, over which relay 50! looks itself, is grounded by relay 405 at contact 441, relay fitbeing energized over the impulsing circuit as before. On energizing, relay 400 locks itself over the holding circuit prepared by relay 403, said circuit extending'irom grounded conductor 260by way of contact-250 of relay 210, conductor 289, contact 43l, contact 44!, contact 449, and upper winding of relay 405 to battery. Y

"Relay v305 energizes over the i pulsing circuit in response to the dialling of the third digit,

conductor 328 of the called. line. If the line is busy there will be a ground potential on the test conductor and testrelay 303 will fail to energize, Thisis' the case also if the testconductor relay 305 over a path which may b traced from grounded conductor :260 by way of'contact 359, contact 345, conductor 419, contact 448, contact 428, contact 281, contact 230,.conductor 211, and

upper winding of busy relay 305 to battery.

Uponfenergizing, r elay 305 locks ,itself to ,con-

ductor 250 at contact 354, opens'theimpulsing circuit at contact 3M, and connects busy tone to trunk conductor 601'at contact .350. The circuit inay; be traced from conductor 6'0'by way of contact 2I5, contact226, condenser 282, con

' tact 245, conductor 251, contact '325,'and contact 355'to the busy tone generator. The callingsubsc'riber is thus given the'liusy signal.

'Ii the calledline is idle there will be a battery potential onthe test "conductor 328, due'to its connection throu'gl'iithewindin'g of cut-off relay 308 to battery. Assuming that the line' is idle when ca-lledfwhen" the relay 305' closes the test circuit during the dialling of the third digit,

the test 'relay 303'energizes and locks itself to grounded conductor 62"at contact 344. The test relay 303' alsoprepares' a, circuitfor relay 304 at contact 345 and at contact 343 places direct ground on the test'co'nductor 328 of thecalled line. The'cut-off relay 308 now energizes and disconnects the line relay 309. j v

When 'relay 306 restores at'th'e end of the third digit it opens the test circuit and closes the prepared circuit of relay 304' at contact 359; Orr-energizing, relay 304 opens the impulsing circuit at contact 341, prepares a circuit for the pick-up relay 30l at contact'348, and closes contacts 346 and '350- in the talking. circuit. This circuit is still open' at contacts of relay 2, but the operationof relay-304 effects the necessary preparation for signalling the-called station. "As previously explained, terminals 348' and 349, Fig. 3, are connected to terminals 508 and 609, respectively, in Fig; 9; When the pick-up interrupter 605 grounds terminal 608, a circuit is completed which'extends'by way of terminals 508 and 348, contacts controlled at contact 324, conductor 299, contact 254, contact 248, conductor 216, contact 348, and winding of pick-up relay 301 to battery. Upon'energizing, relay 30l locks itself at contact 324, sinceterminals 349 and 609 are now grounded at the lock interrupter- 606,"Fig. 9. When the interrupters have made somewhat more than one half of a complete rotation, ground is removed from terminal 509 and relay 30! is deenergized. It energizes again when the'pick-up interrupter 605 grounds terminal 608, from which it will be seen that the 'relay is intermittently energized and deener- .During each ringing period the code inter rupter 6H5 operates the ringing relay 302 over a circuit whichmay betraced from ground-by way of interrupter BIS, conductor B54,'contact 46l of relay 407, conductor 412, contact M of The release of the connectionis under the control of thecalling subscriber. When the receiver counting relay 50L conductor 3 12, contact 320,

being one long ring. The ringing relay 3021energizes each-time its circuit is closed and completes a ringing circuit over the called line which may be traced from the ringing generator by way of conductor 399, contact 3H of relay 30l, contact '34] of relay' 302, contact 3| 2, con- 'ductor 210, contact 25!, conductor 262,.contact 346, contacts of relays 307, 32l,' and M8, conductor 326 of the cal1ed1ine,'the ringerat station' C, line conductor 321, contacts of relays 31a, 32!, and 3131, contact 350,'conduct0r 21s,

contact 255, conductor 2|2, contact 315, contact 342, contact 3H5, conductor 269, and windings of relay 2 l2 to'battery. The exc'hange battery and the ringing generator are connected in series in this circuit, the generator being grounded. The

ringer at station 0 signals the called subscriber each" time the ringing circuit is closed. At the same timethat the called subscriber is signalled a ringing signal is given thecalling subscriber by connecting the generator lead to trunk contluctor 60-at contact 325.;

Relay 2:2 is the ring trip relay andwill not operate effectively, on ringing current" but will 7 1 operate if the receiver at the called station is removed during theringing period. Relay 2l2 will also operate if the receiveris removedduring ia silent period, .When theringi'ngrelay is deenergized. Assuming that the receiver is removed at a time when the ringing relay is deenergized,

the circuit for relay 212 may be traced from ground by way of contact 34!, contact 3I2, conductor 270, contact 25l, conductor 232, contact 346, contacts of relays 301, 321, and M8, line conductor 328, station C, line conductor 321, contacts of relays 3l8, ;32|, and 301, contact 350, conductor 219, contaot 255, conductor v2'12, contact 3I5, contact 342, conductor 269, and'win'ding of relay 2l2 to battery. 7 t

When the ring trip relay 2l2 energizes itfconnects the grounded conductor 63 to relay 2 at contact 256; Upon energizing, relay 2ll locks itself to conductor 260 at contact 253, opens the circuit of the pick-up relay 30] atbontact 254, and completes the talking circuit at contacts 25l l and-255. The latter operation bridges'the bat tery feedrelay 2) across the called line in an obvious manner and this relay'accordingly ener gizes over the called line, the receiver at station C having been removed.

'-is replaced at station A,fthe D. C. bridge' across the calling line is opened and the line relay 204 is deenergized. The line relay breaks the circuit of the release relay 205, which deenergizes an instant later, removing ground from the test conductor 62 and the holding conductor 63, the removal of ground from conductor 62 opening the circuit of relay 201. This relay now deenergizes and removes'ground fromconductor 250. These operations open the holding or locking circuits of all energized relays in the finder and connector and the equipment is restored tonormal. These. restoring operations ,will not be gone over in'detail'fas they will readily be understood from theiexplanation' of the various looking andholding circuits est'ablished'during the setting up of the connection.

. Permanent timing When a line'becomes bridged due to someabnormal cause such as the receiver being accidentally knocked off or the line being short-circuited, a callis i'rlitiate'df-the same as when the receiver is removedbythe' subscriber preparatory to making acalLf Suchj a false call is known as a' permanentif for "it will cause alink circuit to be tied up; indefinitely unless arrangements are provided to-prevent such result. Therelease of 'a link circuit'when'held iby'a permanen will the result that the finder of an idle link circuit I I is operated to connect with the linarexactly as describedin' the case of the subscriber at station A making a regularcall to station C. Assuming t at the first link circuit is' luse'd, the line will be extended to the connector shownin Figs. 2 1305, inclusive, and relays204, 205, and 20 i Will be energized. The interrupters ing the timing of all calls arriving at-link circuits in order to determine if'such-calls are permanentsf or not. The interrupters maybecoritinuouslyrotated'in the direction of the arrows at a speed ofj'about onecom'plete rotation every two minutes, The' interrupters are common toall thecqnnectorsl I When the interrupter altg'rccnds the in Ionfductor acircuitis completed for relay 402,'ex-

When relay 210 energizes it connects the grounded conductor 26!) to the reversing relay 282, which energizes and reverses the incoming nections to 204 and 2 03, thusreversing the direction of current flow over the calling line. .This

"tending rrom ground byway. of4l4, conductor Pl, conductor291, contact 223, conductor 2%, contacts controlled at 423, conductor 294, contact ,zl-ii the circuitmay also be traced to relay twz operation is of no importance in the call being described. Relay 2l0 also opens the lockingcir cuit of relay 405 at contact 250, this relayden-" ergizing and removing ground from the counting relay holding circuit. Relays andMll'v accordingly deenergize. The reversing relay202 opens the locking circuit of relay 403 at contact 224 and'relay 4&3 deenergizes. J

The connection from station to station C has now been completed, the called party has answered the call, and conversation may take place in the usual manner. The talking circuit is conventional and'will not be tracedin detail..

I relays 204, 205fandf201 now release, the latter by Wayofconductor 2184' and contact 430 otrelay 403; Upon energizinggrelay' 402 locks itself at contact-423." ,In'addition, relay 402 disconnects direct ground f rlorn conductor 29l and substitutes conductor -CoG, -which is now grounded at interrupter MB I J V After about two minutes the interrupter M0 removes ground fromconductor CoG. This oper ation" removes ground from conductor 29! f and 4| and SI in the finder. The energized connector relaybreaking the circuit of relay 402. The cut- 41310111, inclusive, are used I for controlling certain timing operations, includ-' the twelfth code for the second code, etc. In view of this explanation it will be understood that the telephone number ofstation D, to which the eleventh code is assigned, is-2861.

When the receiver is removed at station-A- the calling line is extended to the connector of an previously described, and the called station- D* is idle link circuit in the manner already explained.

Assuming that the first link circuit is thefone' used, relaysifit, 265,2.nd 29! are energized. Relay 284, it will berecalled, is the linerelay and is held up over the calling line loop. 1

When the first digit 2 of the' called number is dialled a series of two interruptions'is produced in the calling line, causing the line" relay 26% 'to momentarily deenergize twice and transmit two impulses over the impulsingfoircuit extending to the counting relays. These relaysoperate as previously described, counting relay Etiibeing operated by the first impulse and counting relay 502 by thesecond impulse. At the end of the series of-impulsesrelay-5fi2remains locked Lip-in series withrelay'fl e Relays 3G6 and lllfi 'are energized onthe first impulse and remain energized until the-series'is completed, when both relays fall back. "The e9 energization of relay 30E completes a circuitfor relay M2 which may be traced from; grounded conductor 26!) by way of contact sildconductor 48], contact 455 of rel'ay'tfig, contact't31-contacts controlled at M3,- contact Mill, conductor 494, cntact 5290f relay 5G2, conductor 4%, contact 464, and winding of relay ii2to battery.

.Upon energizing; relay t i 2 locks itself to grounded' conductor 26!], the locking 'circuitextendin'g from conductor 269 by way' of ontacts controlled at 438,,contact 68?; winding of relay 6i i, contact 669, and winding of relay 432 to-battery. Relay 4H does not energize at the nio'mentbe cause it is shunted by direct groundon conductor 499. Until relay All. is energized, relays-M59 and 562 are looked over' a circuit including grounded conductor 260 and 'contacts controlled at 461. This circuit is broken when relay llZ locks itself at contact 487,- and accoidingly relays' 409 and 592 are deenergized,- removing ground from conductor #99 and permitting relay ll I to energize in series with relay 4E2".

Upon energizing, relay 4 "connects relay it? to grounded conductor 269 at contact 452 and'relay 6M energizes. energized by the operation of relay 4-34 following the operation of th units relay, biitr'elay ill remain energized over acirc'uit which estends from the grounded-conductor 26i? by wayoi 'conv tact 258 of relay 2iil,'conductor 289, locking con-- tact of relay 467, and' windin'gof relay 48'! to battery. Relay 1B7 remains energized therefore until relay 2H} energizes upon the answering of the call i It will be understood that on the ip-resentcall the first digit 2 is absorbed in so far-lineselectionis concerned, the only function which is per-formed by the dialling of this; digit being the operation-of relay illi. 'Th'is' relay is the code switching relay, operating to substitute the last,

ten codes for'the firstten, and in practice is provided with ten setsof contactsj Onlyfours'ets are shown in the drawings, due'to lack ofsp'ace;

For the same reason'only one set of contact s is shown completely wired up, thisbeing the set used to switch from code.

To continue with theestablishment of the connection, the connector responds to the-dialling of thedigits 8, 6, and 1 in the "samemanner as Relays 4H and 452 are de'- the first code to the eleventh signalled in the same manner 'as"deseribed;in the case of signalling the station C, except-that now,

remaining operations such as 'ringfcut ofi and release are carried out" in the manner already described. r

v Reverting'call J I I A call from a partly line'subscriber to another subscriber on the same line is known as r a reverting call; The manner in which'such,

calls take place will be described nex it being assumed for this purpose that the subscriber at station A desires to'call the subscriber at-station B. The line number of the line of'stations" A and B is l l and it will be assumed thatthe eighth ringing code isassigned to' station E. Accordingly the complete telephone number of stationB is 118. 1

When the'receiver 'isrernoved 'at 'station A the call is extended'to an available link circuit inthe manner previously described. It will be-again' assumed that the first link circuitxis used. The operationof the finder ofthe first link circuit will therefore extend the calling line to the connector 'shown, and the line relay 294 will be energized and-held over th'ecall-.

Relays ass-anoint of the connec-" ing line. tor are also energized.

When? the calling subscriber dials the first digitl of the called-number thejcounting relay 5M is energized, with the result that the group f Y relayi3l I is operatedoven conductor 384 when 1.

relay 3% falls backat. the end of the digit.

-- When the second digit I -is dialled, the count 1 ing relay 158i is *again energized, causing the operation of the .units' relay 32iJ of the'units relay in thiscase is somewhat different than inthe previous case when it was operated'in response'to the dialling of the digit fiyand accordingly will'be traced. 'Thecircuit is closedwhen relay 365 falls backatthe end of the second digit andextends-frorngrounded conductor 26E) byway of contact 3%, conductor 48!, contact 358 of relaytlfi, contact 43?, contact 443, contact wil, conductor 492 left, contact 433,

conductor- 495," contact 511 of relay- 50!, con ductor; 38L contact 3113, Conductor 383, conductor 3l1,and,w'inding of'relay 32'! to batterm/When relay 32! energizes over the above circuit it connects conductors 3H and 47% with results previously described: a

As the result of the'dialling of the firsttwc digits, therefore,-the group'relay 3H and the units relay' 32! areener'gizedl and line. His

selected and connected With-:T'Ihe controlre lays 405,. 304,. and M3 arealso'QenergizedT- The detailed explanation of how 'these'gresults are brought about has been omitted, but will be understood'readilyirom the previous explanation of the-call from station'A to station C.

When the third. digit 8 is dialled the counting relays respond 'successivelyyuntil relay $88" is energized,=said relay locking :in series with Relay 3% energizes in parallel with" relay 499.

counting 'relayfiilfi and locksi itself' as previously described-. Relaytllt energizes during the-oper- 'ation of thecounting relays'and closes i'the testcircuit including test relay-3ll3'as previously The circuit 232and 221.

the'direc connection betw en conductor "62' and. relayzil'l but conductor remainslconnected to relay 201 by wayof contact 421 of relay- 303 moves direct ground fromthe test conductor.

62 at contact 355, causing relay 205 to enerize. Unon energizing. relay 06 looks itself .at

contact 234 and rounds oonductoriz atconta t 233. al o preparing certain other circuits wh ch will be described.

The calling subscriber, expects to hear the usy si nal, since he. is calling back on his own line. wh ch is busy by reason of the callinith ated at his own station; His instructions. also adv s him that on hearing the busy si nal when mak n a reverting .call he should replace the receiver and await the ringing operation, which will signal the called station and also notify him he the called Subscriber answers the call.

".When the receiver is replaced-at the 09.11-

m station A, the line relay 2! is. deenergized and grounds the test conductor 4 over a circuit which xten s from round by w y Contact lay 3 3. extending fr m rou d d test conduc- W 1 byw y oi c ntact 243, n uctor 214. and lower Winding of relay 303 to. battery. Relay 3B3 energizesbef ore the busy. relay 355M115 back to remove ground from the test conductor 4' at contact-35l, locks itself to conductor 62 at contact 344, grounds test conductor 3' at contact 343, and closes a circuit for relay. 334 at contact 345. Upon energizing, relay 334 comw plates the connection to the calledline at contacts 346 and 3 50, and prepares a circuit for the pickup relay 30] atcontact 348.

2&8, contact 225, contact 23 conductopZfifi,

Qontact! of busy relay-flaconductor 263. ontact 23! of relay ZQGyCORdUGtOI 254, and

contacts of relays 301, MI, and 3. to test con ductor 4. The line relay also opens the'cirult o release relay fllldwhich deener izesafter I vbrief.interval and at contactfll disconnects t i c m n test conductor 62 ircmfground at contact .233 of relay 206. "As just explained,

ho ever. t conductor '4' has been rounded 'by h line relay. and since conductor 4 com nects to conductor 4,, s e Fig. l, the incoming .t stconduotor- 62 remains grounded and the cutoff r ay '5 remains energized. At contact 235, relay 2G5 opens thelocking-circuitcf the busy relay 3B5,'but this relay is slow acting notjre'store, immediately.

-Wh the rel ase relay 205 deone'rgizes it also closes a circuit forv relay 208, extending from grounded conductor 6! by way or Contact 221', ontact-232. conductor 285,; Contact 35:, conductor 268,. andwinding of reverting call rey 308 to batteryQUpon energizing, relay 208 ocks itself to ground d conductor 23c at conact 24,2;a d at s id. contact242 and contact 24! co nects, roundedconductor 260 to the incoming test conductor. 52 by way of contacts At ontact 243; .relay2lla breaks and relay 20! remains energized. At contacts controlled'by. contact 242, relay 208 disconnects unded conduct r 260 from the holding can,

ductor 53, and since ground has. also been re! 'moved from conductor 63. at contact. 2280f re 1m: usy to th all tter. Whcnrelay 2 8 ener-.

sires,v it a sorloso stimuli; for the t st reand does .When the pick-up interrupter 655, Fig. 9, grounds terminals [638 and 348,- the circuit of pick-up relay 33! is completed and this relay locks itselfv at contact 324 to terminal 349,!10 grounded at lock'interrup'ter 309, all as previously described V r r r The eighth code interrupter now grounds the conductor 530 in accordance with the eighth code, selected by the counting relay 538,- and the ringing relay 332 is energized in accordance with said code over acircuit including conductor 530,.con-

tact 53L of relay508, conductor. 3'13, contact-323,

' The ringing generator isugrounded'and accordingly the circuit is completed over the path above traced. The ringer at station B responds to signal the called subscriber.

I Each time theringingrelayenergizesit also connects the ring trip relay 2I2 toline conductor 2 over apath which may be traced from line conductor 2 by way of conductor 2", contacts of relays 3H, 32!, and 301, contact-345, conductor 262, contact 2,5l, conductor 210, contact 3l2, contact 342, contact 316, and conductor 269, the latter conductor connecting to the ring trip relay. Accordingly if the receiveris removed at any station on the line while the ringingrelay is energized the ringing generator and the exchange battery will be connected in seriesthrough thewinding of ring trip relay H2 and this-relay will energize. r

The ringing relay deenergizes one or more times.

while the ringing code is being transmitted. At suchtimes the line conductor 3 is connected to ground at back contact 34I of ringing relay302, while the line conductor 2 is connected to the ring trip relay 212 at back contact 342 of the ringing relay. These circuits canbe readily traced, it being remembered that-relays39l andjflil are energized. It follows that if a receiver is removed at some station in a. silent interval during code transmission, or during the interval between c des,' -the ring trip relay will be energized.

When thetransmissionoi the ringing code is completed, the lock interrupter removes ground from terminals 609 and 349 and the pick-up relay 1 3M is de'energized. An instant later the reverting? call signal interrupter 601 grounds terminals iilll and-H3 for a. short interval, closing another circuit for the ringing relay 302, which extends from 7 ground by way of 601, terminals .610 and 213, contact 240, contact 252, conductor 21 I, contact 323,

V and winding of relay 302 to battery. Upon energizing overthis oircuit,.relay 3.02 closes a circuit for rins ng the bell at station A, said circuit extending iromthe rlngin generator by way of 

